Magnetic encoder, and method and device for producing same

Abstract

Provided is a magnetic encoder that can be produced by a simple modification of an existing production method and that can detect an absolute angle with high efficiency, and a method and an apparatus for producing the magnetic encoder. In a magnetic encoder, a plurality of rows of magnetic tracks, each having N poles and S poles arranged alternately, are disposed adjacent to each other. The rows of magnetic tracks include a main track used for calculating an angle and a sub track used for calculating a phase difference from the main track. The number of magnetic poles of the main track is larger than that of the sub track. The main track is magnetized after the sub track. Thus, accuracy of pitch of the magnetic poles is higher in the main track than in the sub track.

What is claimed is: 
     
         1 . A magnetic encoder comprising:
 a plurality of rows of magnetic tracks disposed adjacent to each other, each track having N poles and S poles arranged alternately, the plurality of rows of magnetic tracks including a main track used for calculating an angle and a sub track used for calculating a phase difference from the main track, the number of magnetic poles of the main track being larger than the number of magnetic poles of the sub track, wherein   accuracy of pitch of the magnetic poles is higher in the main track than in the sub track.   
     
     
         2 . The magnetic encoder as claimed in  claim 1 , wherein the number of magnetic poles of the main track is larger by one than the number of magnetic poles of the sub track. 
     
     
         3 . The magnetic encoder as claimed in  claim 1 , wherein the plurality of rows of magnetic tracks are annularly arrayed. 
     
     
         4 . A method for producing a magnetic encoder comprising a plurality of rows of magnetic tracks disposed adjacent to each other, each track having N poles and S poles arranged alternately, the plurality of rows of magnetic tracks including a main track used for calculating an angle and a sub track used for calculating a phase difference from the main track, the number of magnetic poles of the main track being larger than the number of magnetic poles of the sub track,
 the method comprising:   producing the magnetic encoder that has not been magnetized; and   individually magnetizing the respective magnetic tracks of such un-magnetized magnetic encoder in a sequential order such that the main track is magnetized after the sub track, whereby accuracy of pitch of the magnetic poles is made higher in the main track than in the sub track.   
     
     
         5 . The method for producing a magnetic encoder as claimed in  claim 4 , wherein
 when magnetization of the respective magnetic tracks is performed, the N poles and the S poles are alternately magnetized one by one while shielding, with a magnetic shield, a portion corresponding to a magnetic track that is not currently being magnetized.   
     
     
         6 . An apparatus for producing a magnetic encoder comprising a plurality of rows of magnetic tracks disposed adjacent to each other, each track having N poles and S poles arranged alternately, the plurality of rows of magnetic tracks including a main track used for calculating an angle and a sub track used for calculating a phase difference from the main track, the number of magnetic poles of the main track being larger than the number of magnetic poles of the sub track,
 the apparatus comprising:   a magnetizing yoke configured to magnetize the magnetic tracks of the magnetic encoder that has not been magnetized, the magnetizing yoke having end portions opposing the magnetic tracks;   an exciting coil that is wound around the magnetizing yoke;   a magnetization power source configured to supply a magnetization current to the exciting coil to cause a magnetic flux to pass between the opposing end portions;   a positioning device configured to position the magnetizing yoke relative to such un-magnetized magnetic encoder; and   a controller configured to control the magnetization power source and the positioning device, wherein   the controller controls the magnetization power source and the positioning device so as to individually magnetize the respective magnetic tracks of the un-magnetized magnetic encoder in a sequential order such that the main track is magnetized after the sub track, whereby accuracy of pitch of the magnetic poles is made higher in the main track than in the sub track.